diff --git a/const.go b/const.go
index 1a5a796..6d51f67 100644
--- a/const.go
+++ b/const.go
@@ -200,6 +200,7 @@
 	FLAG_EVENT   = byte(0x20) // for heartbeat
 	SERIAL_MASK  = 0x1f
 
+	DUBBO_VERSION                          = "2.5.4"
 	DUBBO_VERSION_KEY                      = "dubbo"
 	DEFAULT_DUBBO_PROTOCOL_VERSION         = "2.0.2" // Dubbo RPC protocol version, for compatibility, it must not be between 2.0.10 ~ 2.6.2
 	LOWEST_VERSION_FOR_RESPONSE_ATTACHMENT = 2000200
diff --git a/request.go b/request.go
index 5722b44..968372d 100644
--- a/request.go
+++ b/request.go
@@ -219,9 +219,8 @@
 		goto END
 	}
 
+	// https://github.com/apache/dubbo/blob/dubbo-2.7.1/dubbo-remoting/dubbo-remoting-api/src/main/java/org/apache/dubbo/remoting/exchange/support/header/HeaderExchangeChannel.java#L92
 	// dubbo version + path + version + method
-	// org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel
-	// v2.7.1  Line 92
 	encoder.Encode(DEFAULT_DUBBO_PROTOCOL_VERSION)
 	encoder.Encode(service.Path)
 	encoder.Encode(service.Version)
diff --git a/response.go b/response.go
index 17f3528..a1f68ff 100644
--- a/response.go
+++ b/response.go
@@ -58,8 +58,7 @@
 	return NewResponse(body, nil, nil)
 }
 
-// dubbo-remoting/dubbo-remoting-api/src/main/java/com/alibaba/dubbo/remoting/exchange/codec/ExchangeCodec.java
-// v2.7.1 line 256 encodeResponse
+// https://github.com/apache/dubbo/blob/dubbo-2.7.1/dubbo-remoting/dubbo-remoting-api/src/main/java/org/apache/dubbo/remoting/exchange/codec/ExchangeCodec.java#L256
 // hessian encode response
 func packResponse(header DubboHeader, ret interface{}) ([]byte, error) {
 	var (
@@ -332,10 +331,8 @@
 
 var versionInt = make(map[string]int)
 
+// https://github.com/apache/dubbo/blob/dubbo-2.7.1/dubbo-common/src/main/java/org/apache/dubbo/common/Version.java#L96
 // isSupportResponseAttachment is for compatibility among some dubbo version
-// but we haven't used it yet.
-// dubbo-common/src/main/java/org/apache/dubbo/common/Version.java
-// v2.7.1 line 96
 func isSupportResponseAttachment(version string) bool {
 	if version == "" {
 		return false